Referring to FIG. 3 in which a conventional clutch cover assembly is shown applied to a flywheel 11 driven by an engine (not shown), the clutch includes a clutch cover body 12 of a dish-like form having a central aperture of a large diameter. The clutch cover body 12 is provided at the inner periphery with tabs 23, which are fitted into and caulked to substantially rectangular opening 2, having round corners FIG. 4 (called merely as openings hereinafter) in a diaphragm spring 16 to support the diaphragm spring 16 on the clutch cover body 12 by means of wire rings 17, 18, FIG. 3.
The flywheel 11 and the clutch cover body 12 form an internal space 20, in which a clutch disk 13 is concentrically disposed and is connected to an output shaft, only a center line C of which is illustrated. A pressure plate 14 for pressing the clutch disk 13 toward the flywheel 11 is concentrically disposed in the internal space 20 between the disk 13 and the clutch cover body 12.
The diaphragm spring 16 which is formed by an annular metal member is used for pressing the clutch disk 13 onto the flywheel 11 by the pressure plate 14.
The diaphragm spring 16 is integrally provided at the radially outer portion with an annular spring portion 16a, and is integrally provided at the radially inner portion with many radial tongues 5, FIG. 4, extending radially inwardly from the inner periphery of said annular spring portion 16a. These tongues 5 form slits 22 therebetween. The openings 2 are formed radially outside the slits 22.
A pair of metal wire rings 17, 18 having the same radii, are pinched on opposite surfaces of the diaphragm spring 16 by the tabs 23 fitted in the openings 2, respectively.
At the side of the clutch cover body with respect to the diaphragm spring 16 is disposed a release bearing 21, which is slidable along the output shaft and is connected through a link mechanism (not shown) to a clutch pedal, so that it may push the tongues 5 of the diaphragm spring 16 toward the flywheel 11.
In the above structures, when the clutch pedal is depressed, the release bearing 21 pushes the tongues 5 of the diaphragm spring 16 toward the flywheel 11. The annular spring portion of the diaphragm sprig receives a force toward the clutch cover body and, using the wire rings 17 and 18 as fulcrum, releases the pushing force of the spring against the pressure plate 14. Thus, the clutch is released.
In the engaged condition of the clutch, the diaphragm spring 16 elastically presses the pressure plate 14 toward the flywheel 11 again using the wire rings 17, 18 as the fulcrum. The clutch disk 13 is pressed onto the flywheel 11 by the pressure plate 14. The rotational force of the flywheel 11 is transmitted to the clutch disk 13.
However, in the above structures, although the flywheel 11 and the clutch disk 13, as well as the clutch disk 13 and the pressure plate 14, frequently slide on each other to cause friction heat, they do not have a cooling function. The heat generated in the clutch disk 13 causes rapid wear of the clutch disk 13 and, in severe use condition, thermal damage to the friction member and curvature of the pressure plate 14 may result.
In order to cool these friction parts or portions structures, as shown in FIG. 4, in which edges of the tongues 5 of the diaphragm spring 16 are bent, e.g., by press machining, in opposite directions have been proposed for supplying air into the internal space through the slits 22, as shown in arrows A, when the diaphragm spring 16 rotates in the direction X. However, in order to form the tongues 5 of such shape, it is necessary to entirely modify the press dies for forming the tongues, and to form recesses 27 at portions to which the release bearing contacts. Therefore, due to the modification of the press dies, the cost increases and the manufacturing processes are complicated. The object of the invention is to overcome these problems.